Jarðsaga 1

- Saga lífs og lands –Ólafur Ingólfsson

Sedimentary Rocks and Sedimentary Environments

Sedimentary Rocks are the Principal Repository for Information About the

Earth’s Past Environment

Earth’s history largely read from sedimentary strata

SedimentaryRocks

IgneousRocks

MetamorphicRocks

Magma

Sediment

Pressure And Cementation

Erosion

Erosion

Heat and Pressure

CoolingHeat

Heat

Pressure Eros

ion

Sedimentary RocksClastic Rocks (molaberg)• Made of Fragmentary Material • Deposited by

– Water (Most Common) – Wind – Glacial Action – Gravity

Chemical-Biological Sedimentary Rocks

• Evaporation • Precipitation • Biogenic Sediments

Sedimentary Rocks

Clastic Rock – composed of fragments of preexisting rocks.

Nonclastic Rock – composed of chemical precipitates or biogenic

matter.

Sediment Sizes and Clastic Rock Types

Grain SizeSedimentRock Type

1mm +GravelConglomerate.01-1 mmSandSandstone.001-0.1 mmSiltSiltstoneless than 0.001 mmClayShale

Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks.

Clastic Sediment Size

Some Special Clastic Rock Types

• Arkose Feldspar-Rich • Breccia Angular Fragments • Graywacke Angular, Immature

Sandstone

Classification of ClasticSedimentary Rocks

Major types of sandstone based on mineral/rock contentGreywackeQuartzite Arkose Lithic Sandstone

Chemical-Biological SedimentsEvaporites -Water

Soluble• Halite • Gypsum • Calcite Precipitates• Gypsum • Limestone • Iron Formations

Alteration After Deposition

• Limestone ⇨ Dolomite Biogenic Sediments• Limestone - Shells,

Reefs, Etc. Organic Remains• Coal • Petroleum

Biogenic SedimentsTerestrial Sediments - mainly plant matterMarine Sediments - mainly carbonatesCorals - Large components of reefs.Bivalves, Gastropods (sníglar), Foraminifers (götungar) - Whole or partial skeletons form sand and gravels.Algae, Crinoids (sælilja), Echinoderms (skrápdýr), Bryozoans (mosadýr) -disintergrate to form some sand particles and lime mud.Diatoms (kísilþörungar), Radiolaria (geislungar)– Bedded chert SiO2

Conglomerate (völuberg) Sandstone

Shale (leirskífur) Limestone (kalksteinn)

Limestone Gypsum

Coal

Arkose

Some major types of

sedimentary rocks

Environmental Clues in Sedimentary Rocks

• Grain Size - Power of Transport Medium

• Grading - Often Due to Floods • Rounding • Sorting • Cross-bedding - Wind, Wave or

Current Action

} Transport, Reworking

fossil fish

Sand grains show evidenceof transport

ripple marks formed bywind or wave action

Mud cracks

Features in sedimentary rocks

Bedding or Stratification• Almost Always Present in Sedimentary

Rocks • Originally Horizontal • Tilting by Earth Forces Later • Variations in Conditions of Deposition • Size of Beds (Thickness)

– Usually 1-100 cm – Can Range From Microscopic to 50m

• Sedimentary rocks commonly show layering that form as sediment is deposited– Stratification (lagskifting)– cross bedding (skálögun)– graded bedding (lóðgreining)

Sedimentary structures

Cross bedding is formed by the migration ofsand waves (ripple marks or dunes) by sand particlestravelling up the windward face and depositing down the leeward face

wind wind Migration of the dune

leewardwindward

Graded bedding

• Graded bedding can be produced by turbidity currents, which can travel up to 100 km/hr– currents can be started by

landslide or earthquake down the continental slope

– deposition based on density (gravity) and settling velocity

As the current slowsthe coarse grains aredeposited first,followedby successively finer-grained sediments

Environmental Clues in Sedimentary Rocks

• Fossils – Salt Water - Corals, Echinoderms (skrápdýr)– Fresh Water - Insects, Amphibians – Terrestrial - Leaves, Land Animals

• Color And Chemistry – Red Beds - Often Terrestrial – Black Shale - Oxygen Poor, Often Deep

Water– Evaporites – Arid Climates

Each kind of sedimentary environmenton Earth’s surface is characterized by

particular kinds of sediment and patterns of bedding

• Sediments are deposited in a variety of places.

• Each is characterized by a combination of the kind and amount of water, the local topography, and the biological activity.

• These in turn are related to plate tectonic setting and climate.

• Although sediment can be deposited anywhere, large accumulations of sediment are not, being found in only a handful of environments.

Common Sedimentary Environments:

Non-marine environmentsStream sediments, Lake sediments, Glacial (ice deposited) sediments, Eolian (wind deposited) sediments

Continental Shelf sedimentsEstuarine sediments, Deltaic sediments, Beach sediments, Carbonate shelf sediments, Marine evaporite sediments

Continental slope and rise sedimentsTurbidites, Deep Sea Fans, Sediment drifts

Deep Sea SedimentsDeep -Sea oozes, Land-derived sediments

Major sedimentary environments

• weathering - physical and chemical• transportation - wind, water, and ice

– sorting• deposition

alluvialfan

dunes glacier

fluvial

beachdelta

tidalflat

barrierisland

organicreef

deep marineShallow marine

organic reef

lake

• Sedimentary environmentsencompass the physical, chemical, and biological conditions in areas where sediment is deposited. These comprise three distinct groups: 1) continental, 2) shoreline (transitional), 3) marine

Sedimentary Environments

Continental (land-based) EnvironmentsAlluvialDesertLakeGlacial

Shoreline EnvironmentsDeltaicTidal flatBeachMarine EnvironmentsContinental shelfContinental slopeOrganic reefsDeep-sea

Rounded-----Rounded toangular

AngularGrain Shape

SandClay to silt orsand (Coarsening upward)

Clay to gravel(Fining upward)

Clay to gravelGrain Size

GoodVariableVariablePoorSorting

Terrigenous orevaporite

Terrigenous, carbonate, or evaporite

TerrigenousTerrigenousComposition

Quartz arenite(sandstone) or gypsum

Siltstone, shale,limestone or evaporites

Conglomerate, sandstone, siltstone, shale

Breccia, conglomerate, arkose

Rock type

DunesLacustrineFluvialAlluvial Fan

SedimentaryStructures

Cross-beddingSymmetricalripples, lamination, cross-bedding, graded bedding

Asymmetricalripples,cross-bedding,graded bedding,tool marks

Cross-beddingand graded bedding

Continental sedimentary environments – Classification Chart

(http://www.dc.peachnet.edu/~pgore/geology/historical_lab/environmentchart.htm)

Transitional sedimentary environments

Marine shellsMarine shellsMarine shellsPlant fragments, shells

Fossils

Stromatolites, trails, tracks, burrows

Trails, burrows

Tracks, trails, burrows

Trails, burrows

Organic or Biogenic Sedimentary Structures

Lamination, mudcracks, ripples, cross-bedding

Lamination, ripples, cross-bedding

Cross-bedding, symmetrical ripples

Cross-bedding, graded bedding

Inorganic Sedimentary Structures

VariablePoorGoodPoorSorting

------Rounded to angular

---Grain ShapeClay to siltClay to siltSandClay to sandGrain Size

Terrigenous, carbonate, or evaporite

Terrigenouscarbonate, or evaporite

Terrigenousor carbonate

TerrigenousComposition

Siltstone, shale, calcilutite, dolostone or gypsum

Siltstone, shale, limestone

Quartz arenite, coquina

Sandstone, siltstone, shale, coal

Rock Type

TIDAL FLATLAGOONBARRIER BEACHDELTA

Marine sedimentary environments

Marine shells, rare plant fragments

Marine shells Corals, marine shells

Fossils

Trails, burrowsTrails, burrows---Organic or Biogenic Sedimentary Structures

Graded bedding, cross-bedding, lamination, flute marks, tool marks (turbidites)

Lamination, cross-bedding

---Inorganic Sedimentary Structures

PoorPoor to good---Sorting---------Grain Shape

Clay to sandClay to sandVariable, framework, few to no grains

Grain Size

Terrigenous or carbonateTerrigenous or carbonate

CarbonateComposition

Litharenite, siltstone, and shale (or limestone)

Sandstone, shale, siltstone, fossiliferouslimestone, ooliticlimestone

Fossiliferouslimestone

Rock Type

CONTINENTAL SLOPE AND RISE

CONTINENTAL SHELFREEF

Continental glacier system

• Continental glaciers greatly modify the entire landscape they cover. Flowing ice removes and transports soil and bedrock, and transports it long distances. Supraglacial

debris

plucking abrasionsubglacial till

moraine

proglaciallake

Surface tiltstowards glacier

outwashplain

Isostatic subsidence

iceberg

dropstones

Glacial landforms and

sedimentsGlacial till Glacial varves

Moraine terrain Esker

drumlin outwash plain

• Geologicalfingerprinting of continental scaleglaciations is veryimportant in paleogeographical reconstructions –

• Distribution of glacial tills used earlyon to argue for Continental Drift

The glacial environment

Margins of a valleyglacier in Canada

Ancient glacial sediments(diamictite) in Utah

Minor delta in theGreat Bear Lake, Canada

Ancient delta depositin the Colorado Plateau

The delta environment

• Glaciers generally create poorly sorted sedimentary rocks

• Deltas (óseyri)form a variety of rock types, depending on the environment of deposition.

Deltas• The history of the Mississippi delta involves repeated

switching of the main channel. Previous deltas are numbered (1-6) by age from oldest to youngest.

River systems and tectonics

• The evolution of the major rivers of the world is influenced directly and indirectly by plate tectonics.

The fluvial environment• Rivers are the major channels by which erosional debris

is transported from the continents to the oceans.• River deposits are characterized by channels of sand or

gravel. • River deposits are typically graded due to channel

migration and a decrease in flow energy

Point bar deposits ina meandering river

Ancient stream channelin Utah

River systems

The evolution of stream meanders

• Running water is by far the most important agent of erosion. Other agents, such as groundwater, glaciers, and wind, are locally dominant but affect only limited parts of the Earth’s surface.

The major features of a floodplain

• In the lower parts of the drainage system, the gradient of a river is very low. As a result the velocity of the river is reduced and deposition of much of the sediment load occurs, to create– Floodplains (flæðiland)– alluvial valleys (árdalir)– Deltas (óseyrar)– alluvial fans (árkeilur)

The eolian (wind) environment

Modern alluvial fanin Death Valley, CA

Ancient alluvial fandeposit in Utah

Modern sand dunesin the Sahara Desert

Ancient dune depositsin Zion National Park

• Wind is a very effective sorting agent separating mud, silt, and gravel from sand

Alluvial Fans

The desert environmentDeserts should more correctly becalled arid regions. Arid and semi-arid regions characteristically receiveless than 50-100 mm of precipitation/year, and often the amount of evaporation is greater than the amount of rainfall. One-third of the earth's land mass is arid to semiarid (either desert or semidesert).Locations of deserts have changedthroughout geologic time as theresult of continental drift and theuplifting of mountain ranges. Modern desert regions are centered between 15 and 30 degrees north and south of the equator and in the Polar regions

Sorting by Wind

Enormous loess deposits, composed of long-transported aeolian silt, common on continents – China

Wetlands environments

It is no accident thatriver valleys and theirfloodplains have beenthe focus of humancivilisations for over6,000 years. This simply reflects the key role that water and wetlands have played throughout the development of life on planet Earth.

The beach and lagoon

environments

A modern beach on the Atlantic coast

An ancient beach deposit in Utah

A lagoon along USAAtlantic coast

Ancient lagoon depositsin eastern Wyoming

• Much sediment accumulates in zones where land meets the sea; the type of sedimentary rock formed is dependent on the energy of the fluid environment.

Shoreline systems

• Shorelines are dynamic systems involving the energy of waves andcurrents.

• Wind-generated waves provide most of the energy for erosion, transportation and deposition of sediment.

• Waves approaching a shore are bent, or refracted, so that energy is concentrated on headlands and dispersed in bays

Deposition along coasts

• Sediment transported along the shore is deposited in areas of low wave energy, and results in various landforms– beaches– spits– barrier islands

Output to beaches

Output tobackshore dunes

Output to spits and bars

Output to deep water

Input from cliff erosion

Input from rivers

A barrier island can form by the migration of a spit

The tidal flat and reef

environment

Modern tidal flat inthe Gulf of California

Ancient tidal flat deposit in Utah

An organic reef onMoorea near Tahiti

Ancient Devonian reefin Australia

• Tidal flats (leirur)are alternately covered with shallow water and exposed to air. • Organic reefs are solid structures of calcium carbonate constructed of shells and secretions of organisms.

• Reefs form a unique coastal feature since they are biological in origin.

• Modern reefs are built by a complex community of coral, algae, sponges and other marine invertibrates

• most reefs grow in warm, clear, shallow waters in tropical regions

Volcanic island surroundedby a fringing reef

Reef mounds arevisible through theshallow waters in thelagoon

The global distribution of modern coral reefs

Community oforganisms in a reef

Types of reefs

• Fringing reefs (jaðar-)

• Barrier reefs (hindrunar-)

• platform reefs (pall-)

• atolls (hringey) -ring structured reef.

• Darwin was first to propose how an atoll might have formed, in 1842 on the voyage of the Beagle.

A fringe reefs first begins to grow along the coast of a newly-formed volcanic island

As the island subsides, the reef grows upward and develops a barrier separating the lagoonfrom open water

Further subsidence completely submerges the island while thereefs continues to grow

The shallow and deep marine environment

The shallow marineenvironment in theBahamas

Ancient shallow marinesediments in Kansas

Seismic reflection of deep sea fans off the Indian coast

Ancient turbidites on the southern coast ofFrance

• Shallow marine environments border most land area, forming sandstones, shales, and limestones. • Deep ocean sediments are derived from turbidites and the constant rain of carbonate and silica from shallow oceans.

Shallow-marine andcontinental shelf

environmentOpen continental shelvesdisplay a variety of physicalconditions and therefore produce a variety of sedimentary deposits.

• Tidal currents and wavemotion produce sandy bottoms

• On more quiet shelves, muddy sands accumulate

Very importantenvironment for

development of life!

Sea expands over the land(transgression)

Sea moves back from the land(regression)

sand mud

lime

Exposure of a transgressiveregressive cycle

shoreline

Stratigraphicsequences

- example of a transgression-

regression cycle

Interpretation of ancient sedimentary environments

Alluvialfan River

DeltaLagoon

Barierisland Shallow

marine

LimestoneShaleSandstoneCoalConglomerate

• Sedimentary rocks are products of the hydrologic system and interaction with Earth’s crust.

• They provide a record of changing surface environments.• Plate tectonics has a profound influence on the origin of

sedimentary rocks.• Each tectonic setting produces a distinctive sequence of

sedimentary rocks.

Stratigraphical mapping

- The purpose of stratigraphical mapping is to get a sense of the physical and petrographicproperties of rocks and interpret in terms of geological events or environments -

Lithostratigraphy:Describes and defines units of rocks on the basis of lithological characteristics.

Unit boundaries, textures (samsetning), structures (bygging), fossils

Additional reading, some good web-sites, references used when prepating this lecture:

Stanley: Earth System History, chapter 5.http://www.virtual-geology.info/FILTER/intro.html#templateshttp://gpc.edu/~pgore/geology/historical_lab/environmentchart.htmhttp://www.es.ucsc.edu/~jsr/EART10/Lectures/HTML/lecture.05.htmlhttp://www.bhc.edu/academics/science/harwoodr/Geol101/study/sediment.htmhttp://www.amateurgeologist.com/content/glossary/rock/sedimentary.html#sedimentaryhttp://www.homepage.montana.edu/~esci111/RockCycle-1/sedimentary.htm#clastichttp://csmres.jmu.edu/geollab/Fichter/SedRx/SedEnvir.html#sedenvirhttp://www.uwgb.edu/dutchs/EarthSC202PowerPoint/5http://www.uic.edu/classes/geol/eaes350/1http://www.surrey.ac.uk/eng/InfoPoint/downloads/civ/SE1122/1http://www.volcanoworld.org/vwdocs/vwlessons/lessons/Sedrocks/Sedrocks1.html